Abstract
Pear-shaped cells and“vesicle-rich cells”in the epithelium of pyloric caeca of the rainbow trout, Salmo gairdneri, were examined mainly with the electron microscope.
1.Pear-shaped cells are faced on the epithelial lumen of the pyrolic caecum and separated from the basement membrane of the epithelium.They are provided with a small number of microvilli on the apical surface and connected with the neighboring epithelial cells by the junctional complex.The most conspicuous features are the encasing of the endoplasm with a layer of the finely filamentous material (corresponding to the ectoplasm or cytoplasmic capsule) measuring from about 700 to 850 mic in thickness just beneath the plasma membrane, provided with several tens of the membrane-bound rodlets in the central region of the cells, and showing mitochondrian concentration in great numbers in the upper part of the cells.
In the basal portion of the pear-shaped cells there is an indistinct or almost absent region of the cytoplasmic capsule where there appear several cored vesicles 900-1000 Å, .in size, various profiles of the rough endoplasmic reticulum with very sparse ribosomes and glycogen granules.Most nuclei of the pear-shaped cells in longitudinal sections take a horse-shoe shape and are located eccentrically in the base.Golgi apparatus, contiguous to the nucleus, consists of lamellae, many vesicles and an occasional vacuole.Cisternae of the rough endoplasmic reticulum show various vacuolized profiles with very sparse ribosomes on their outer sides.
Each rodlet consists of an oval ampulla and a long process extending toward the apical region of the pear-shaped cell.The process is projected from the ampulla but never into the pyloric caecum lumen.An electron-opaque axis originating from the ampulla runs the central part of each process.A number of cored vesicles 900-1000Å.in size tend to concentrate around the boundary between the ectoplasm (or cytoplasmic capsule) and endoplasm in the mitochondria-concentrated area, and they seem to be formed in tubular profiles of the smooth endoplasmic reticulum.
2.Pear-shaped cells are neither parasitic cells such as Rhabdospora thelohani, nor a life cycle form of goblet cells, nor wandering cells such as granular leucocytes and lymphocytes.
3.Several cells of a new type were found by electron microscopy in the epithelium of the pyloric caecum, close to the pear-shaped cell or singly, and were named as a “vesicle-rich cell”.The majority of cisternae of the rough endoplasmic reticulum show various vesicular profiles with very sparse ribosomes and contain the moderately electron-opaque flocculent or finely granular material.Flattened cisternae of the smooth endoplasmic reticulum wind in various directions forming a double or triple lamella whose development is different from cell to cell, and they are located also in the cytoplasm of the infranuclear area near the basement membrane.Morphological findings characteristic of Golgi complex except for the above-mentioned winding lamellae, however, have not been found, and therefore it is difficult to determine whether the lamellae can be identified with the Golgi lamellae.
